The philosopher David Lewis is credited by many social scientists, including mainstream economists, with having founded the modern (game-theoretical) approach to conventions, viewed as solutions to recurrent coordination problems. Yet it is generally ignored that he revised his approach, soon after the publication of his well-known book. I suggest that this revision has deep implications (probably not perceived by Lewis himself) on the analytical links between coordination, uncertainty and rationality. Thinking anew about these issues leads me to map out an (...) alternative social scientific research programme. The traditional ontological equipment of methodological individualism should be reinforced in order to admit the existence of an “intersubjective” world beside the two familiar worlds: the “objective” world of observable things, and the “subjective” world of expectations and individual beliefs. In particular, language becomes necessary to understand coordination via conventions, rather than the other way round. That has led a group of institutionalist economists and pragmatist sociologists to develop an enlarged model of rationality, no longer isolated from questions of coordination and values. This model is the basis for the “Economics of Conventions”. (shrink)